Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.32	3.566%	$232.3193	$232.32	$232.30	$232.30
Purchase #2	$50.68	8.349%	$54.9113	$54.91	$54.90	$54.90
Purchase #3	$55.46	7.365%	$59.5446	$59.54	$59.55	$59.50
Purchase #4	$100.34	10.141%	$110.5155	$110.52	$110.50	$110.50
Purchase #5	$147.87	8.761%	$160.8249	$160.82	$160.80	$160.80
Purchase #6	$67.35	4.576%	$70.4319	$70.43	$70.45	$70.40
Purchase #7	$70.75	10.326%	$78.0556	$78.06	$78.05	$78.10
7 purchase totals =	$716.77		$766.6031	$766.60	$766.55	$766.50